You can generate a log file whenever the you do the reload.
There is an option in document properties as "Generate Log file" which you can find under the Settings menu.
During the reload, it will write the doc name, start and end time of execution, user name, no of rows fetched from the qvd or source file and so on.
It is even possible to identify in which line number the error is caused if anything occurs during the execution.
Hope this helps you.
Yes, As Andrew said that logs are genrated for reloads and it will have all the info you require. (Opening a doc will not create/edit a log file.)
Normally log file will contain logs only for last reload but if you want to keep old logs also then you can use Timestamp in log file's name. Check box for this is given just below the option of "Generate Log file" in Document properties.